The impact of sea surface waves on air-sea fluxes of heat and momentum over the Yellow Sea caused by cold fronts during cold air outbreak(CAO)events is investigated through numerical experiments with a FVCOM-SWAVE(Fin...The impact of sea surface waves on air-sea fluxes of heat and momentum over the Yellow Sea caused by cold fronts during cold air outbreak(CAO)events is investigated through numerical experiments with a FVCOM-SWAVE(Finite-Volume Coastal Ocean Model-Surface WAVE)wave-current coupled model.Two typical types of cold fronts,i.e.,those respectively from the north and from the west,are simulated and compared to each other and with monthly mean.During cold seasons,currents in the Yellow Sea are weaker than that during warm seasons.As a result,waves show a more prominent impact.The numerical simulations suggested that both the heat and momentum fluxes are significantly enhanced during CAO events;and they could be a few times larger than the monthly average of a five-year mean.The enhancement is highly sensitive to the features of CAOs.Specifically,it depends on the cold front orientation,intensity and evolution.One mechanism that strengthens the two fluxes is via sea waves.For the CAOs that are studied,an increase in sea wave height by 50%can double the maximal momentum flux,and cause an increase in heat flux by 10-160 W/m^2.展开更多
From 26 November to 1 December 2022,intense cold air masses swept across China from northwest to south,resulting in a nationwide cold air outbreak(CAO)case characterised by drastic and sudden temperature drops with ra...From 26 November to 1 December 2022,intense cold air masses swept across China from northwest to south,resulting in a nationwide cold air outbreak(CAO)case characterised by drastic and sudden temperature drops with rain,snow and strong winds.The physical processes that dominate the intensification of the cold air masses during this CAO event remain unclear.In this study,the evolution of the CAO case,which is indicated by the dry static energy(DSE),is investigated using a novel approach in the framework of Lagrangian backtracking.The dominant processes can be identified by decomposing the DSE change into four diabatic heating terms due to shortwave radiation,longwave radiation,latent heat and turbulent processes.Overall,in this case,most of the cold air parcels originated from the east of Novaya Zemlya and crossed Central Siberia before reaching China.Thus,these air parcels mainly manifested on the northwest‒southeast path.The duration of the cold air intensification differed between subregions.The cold air parcels experienced long cooling periods(approximately 9 d)before reaching northern China(i.e.Northwest,North and Northeast China),whilst the southern parts(i.e.Central,East and South China)underwent relatively short cooling periods(6-8 d).Accordingly,the cold air affecting northern China is more intense than that affecting the southern parts,especially for East and South China.For all six subregions,longwave radiative cooling is identified as the dominant contributor to the cold air intensification,and the latent heat processes as the secondary contributor.The weakening of cold air parcels as they approach and pass over these regions is driven by turbulent processes and shortwave heating.Central Siberia and Lake Baikal are identified as key areas for the intensification of cold air passing over both regions.In addition,air parcels affecting Northwest China are intensely cooled as they pass over the Junggar Basin,while the North China Plain is a key area for cooling air parcels reaching Central,East and South China.From a Lagrangian perspective,these findings provide insights into the physical processes driving the behaviour of cold air parcels,which would help understand the mechanisms involved in the past changes and future projections in CAOs.展开更多
Ambient SO2 concentration at a high rain fall site, Shillong (25.67oN, 91.91oE, 1064 m ASL), located in North-East India, was measured during March 2009 and January 2010 with the aim to understand the effect of long r...Ambient SO2 concentration at a high rain fall site, Shillong (25.67oN, 91.91oE, 1064 m ASL), located in North-East India, was measured during March 2009 and January 2010 with the aim to understand the effect of long range transport of pollutants from North-East Asia on the ambient SO2 levels at this relatively clean site. The concentrations recorded during the former sampling period were very high (Max: 262.3 ppb)—which decayed down gradually towards the end the sampling period—whereas those during the latter sampling period were well within the acceptable limits (Max: 29.7 ppb). This elevated SO2 concentrations during March 2009 is proposed to have association with a major cold air outbreak and an associated cyclone preceding one of the dust storm events reported in China, and a resultant sudden change in wind trajectory leading to the long range transport of pollutants to the sampling site. The argument is formulated on the basis of the back trajectory analysis performed using HYSPLIT for the month of March 2009—the plots clearly showed a drastic change in wind trajectories between 8th and 15th of March 2009 wherein the winds traveled over some of the highly polluted regions such as the Perm region of Russia—and on the results from model runs performed using the global 3-D model of tropospheric chemistry, GEOS-Chem (v8-03-01)—it clearly showed the tropospheric SO2 over Perm region in Russia peaking during Nov, Dec, Jan, Feb and Mar every year, possibly due to central heating. The observation of long range transport of SO2 from the highly industrialized areas of Perm in Russia to North-East India during dust storm events has important implications to the present understanding on its relative contribution to the Asian pollutant outflow to the Pacific during spring as the GEOS-Chem model runs also showed regions in and around Russia with relatively high concentrations of atmospheric NOx, Peroxyacetyl Nitrate, Lumped Peroxypropionyl Nitrate, HNO3, HNO4,C3H8, C2H6, SO4, NH4, Inorganic Sulphur Nitrates and Lumped Alkyl Nitrate.展开更多
基金supported by the National Natural Science Foundation of China (Grant Numbers. 41276033)the Jiangsu Science and Technology Support Project (Grant Number. BE2014729)+1 种基金the support from Jiangsu Provincial Government through Jiangsu Chair Professorshipthe 2015 Jiangsu Program of Entrepreneurship and Innovation Group
文摘The impact of sea surface waves on air-sea fluxes of heat and momentum over the Yellow Sea caused by cold fronts during cold air outbreak(CAO)events is investigated through numerical experiments with a FVCOM-SWAVE(Finite-Volume Coastal Ocean Model-Surface WAVE)wave-current coupled model.Two typical types of cold fronts,i.e.,those respectively from the north and from the west,are simulated and compared to each other and with monthly mean.During cold seasons,currents in the Yellow Sea are weaker than that during warm seasons.As a result,waves show a more prominent impact.The numerical simulations suggested that both the heat and momentum fluxes are significantly enhanced during CAO events;and they could be a few times larger than the monthly average of a five-year mean.The enhancement is highly sensitive to the features of CAOs.Specifically,it depends on the cold front orientation,intensity and evolution.One mechanism that strengthens the two fluxes is via sea waves.For the CAOs that are studied,an increase in sea wave height by 50%can double the maximal momentum flux,and cause an increase in heat flux by 10-160 W/m^2.
基金supported by the National Nature Science Foundation of China(41875119 and 42005118)the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)(2642023095)+1 种基金Science and Technology Development Plan in Jilin Province of China(20230203135SF)Open Research of State Key Laboratory of Severe Weather(2022LASW-B05).
文摘From 26 November to 1 December 2022,intense cold air masses swept across China from northwest to south,resulting in a nationwide cold air outbreak(CAO)case characterised by drastic and sudden temperature drops with rain,snow and strong winds.The physical processes that dominate the intensification of the cold air masses during this CAO event remain unclear.In this study,the evolution of the CAO case,which is indicated by the dry static energy(DSE),is investigated using a novel approach in the framework of Lagrangian backtracking.The dominant processes can be identified by decomposing the DSE change into four diabatic heating terms due to shortwave radiation,longwave radiation,latent heat and turbulent processes.Overall,in this case,most of the cold air parcels originated from the east of Novaya Zemlya and crossed Central Siberia before reaching China.Thus,these air parcels mainly manifested on the northwest‒southeast path.The duration of the cold air intensification differed between subregions.The cold air parcels experienced long cooling periods(approximately 9 d)before reaching northern China(i.e.Northwest,North and Northeast China),whilst the southern parts(i.e.Central,East and South China)underwent relatively short cooling periods(6-8 d).Accordingly,the cold air affecting northern China is more intense than that affecting the southern parts,especially for East and South China.For all six subregions,longwave radiative cooling is identified as the dominant contributor to the cold air intensification,and the latent heat processes as the secondary contributor.The weakening of cold air parcels as they approach and pass over these regions is driven by turbulent processes and shortwave heating.Central Siberia and Lake Baikal are identified as key areas for the intensification of cold air passing over both regions.In addition,air parcels affecting Northwest China are intensely cooled as they pass over the Junggar Basin,while the North China Plain is a key area for cooling air parcels reaching Central,East and South China.From a Lagrangian perspective,these findings provide insights into the physical processes driving the behaviour of cold air parcels,which would help understand the mechanisms involved in the past changes and future projections in CAOs.
文摘Ambient SO2 concentration at a high rain fall site, Shillong (25.67oN, 91.91oE, 1064 m ASL), located in North-East India, was measured during March 2009 and January 2010 with the aim to understand the effect of long range transport of pollutants from North-East Asia on the ambient SO2 levels at this relatively clean site. The concentrations recorded during the former sampling period were very high (Max: 262.3 ppb)—which decayed down gradually towards the end the sampling period—whereas those during the latter sampling period were well within the acceptable limits (Max: 29.7 ppb). This elevated SO2 concentrations during March 2009 is proposed to have association with a major cold air outbreak and an associated cyclone preceding one of the dust storm events reported in China, and a resultant sudden change in wind trajectory leading to the long range transport of pollutants to the sampling site. The argument is formulated on the basis of the back trajectory analysis performed using HYSPLIT for the month of March 2009—the plots clearly showed a drastic change in wind trajectories between 8th and 15th of March 2009 wherein the winds traveled over some of the highly polluted regions such as the Perm region of Russia—and on the results from model runs performed using the global 3-D model of tropospheric chemistry, GEOS-Chem (v8-03-01)—it clearly showed the tropospheric SO2 over Perm region in Russia peaking during Nov, Dec, Jan, Feb and Mar every year, possibly due to central heating. The observation of long range transport of SO2 from the highly industrialized areas of Perm in Russia to North-East India during dust storm events has important implications to the present understanding on its relative contribution to the Asian pollutant outflow to the Pacific during spring as the GEOS-Chem model runs also showed regions in and around Russia with relatively high concentrations of atmospheric NOx, Peroxyacetyl Nitrate, Lumped Peroxypropionyl Nitrate, HNO3, HNO4,C3H8, C2H6, SO4, NH4, Inorganic Sulphur Nitrates and Lumped Alkyl Nitrate.
